In recent years, various vehicle lighting units including headlights utilizing a semiconductor light emitting device as a light source have been proposed, for example, such as those disclosed in Japanese Patent Application Laid-Open No. 2010-277818.
As shown in FIG. 1A, a conventional vehicle lighting unit 200 disclosed in the above publication includes a light source 210 utilizing a semiconductor light emitting device such as an LED, a projection lens 220 disposed in front of the light source 210, etc.
In the vehicle lighting device 200 with the above configuration, the light emitted from the light source 210 and projected forward through the projection lens 220 can form a basic light distribution pattern Pa as illustrated in FIG. 1B, diffused in the horizontal direction below the horizontal line H.
When the vehicle lighting unit 200 with the above configuration uses as the light source 210 a light source that uses a combination of a semiconductor light emitting device (such as a blue LED) and a light-transmitting member (such as a yellow YAG phosphor) covering the light emitting device, such as those disclosed in Japanese Patent Application Laid-Open Nos. 2012-134355, 2011-204376, and 2010-93208), a problem or characteristic may arise in which the chromaticity of the basic light distribution pattern Pa partially falls outside the white range as determined under a provision of law or the like (for example, JIS D5500).
When a light source with a combined structure of a semiconductor light emitting device and a light-transmitting member covering the light emitting device is used, the blue light emitted from the semiconductor light emitting device and directed in an optical axis (for example, a normal direction to the light emission surface of the semiconductor light emitting device) may travel a shorter distance through the light-transmitting member when compared with the blue light directed in an oblique direction to the optical axis. As a result, the blue light directed in the normal direction may not be sufficiently absorbed by the phosphor, and not converted to yellow light. This phenomenon may cause the above characteristics and/or problems.